Fuel feed system for a gasifier

ABSTRACT

A fuel feed system for use in a gasification system includes a feed preparation section, a pressurization and conveyance section, and a slag additive section. The feed preparation section is configured to grind the fuel to a predetermined size and to adjust the moisture content within the particulate fuel. The pressurization and conveyance section is coupled in flow communication with the feed preparation section, and includes at least one solids pump configured to receive a flow of the particulate fuel at a first pressure and discharge the particulate fuel at a second pressure. The slag additive section is configured to feed a slag additive mixture into the gasifier and to substantially control the total water content within the gasification system.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to and the benefit of the filing dateof U.S. Provisional Application No. 60/982,967 filed on Oct. 26, 2007,which is hereby incorporated by reference in its entirety.

BACKGROUND

The field of the disclosure relates generally to gasification, such asgasification used in Integrated Gasification Combined Cycle (IGCC) powergeneration systems, and more specifically to systems for supplying highmoisture content, solid, carbonaceous fuels to gasifiers, and methods ofstart-up for such systems.

At least one known IGCC plant feeds a water-based slurry of bituminouscoal to a refractory-lined, entrained flow gasifier to generate the fuelgas used in power generation. Such a slurry feed system may provide aneconomical and reliable option for feeding higher rank coals, such asbituminous and anthracite coals, to the gasifier. However, such a systemis less attractive for lower rank coals, such as sub-bituminous coals,because of the difficulty surrounding the production of low rank coalslurries with a solids concentration and energy content high enough forefficient power production.

Inherent moisture is water trapped in the pores of the coal andtherefore such moisture may not be available for making the coal slurry.Low rank coals have a relatively higher inherent moisture content (e.g.22-30 wt %) than compared to high rank coals (e.g. <10 wt %). In knownIGCC systems, producing coal-water slurry represents a physical processthat includes suspending the coal particles in water to facilitateenabling the coal particles to freely move past one another, i.e.enabling slurry flow within the IGCC system. More specifically, in someknown IGCC systems, water may be added in an amount sufficient toproduce a slurry with a viscosity no higher than about 700 to 1000Centipoise to enable the slurries to be screened, pumped and sprayed bythe feed injectors. Coals with higher inherent moisture contentnaturally produce slurries with higher total water content. For example,coals with relatively higher inherent moisture content produce slurrieswith a lower solids content, i.e. lower energy content per unit volumeof slurry. While water may be added to particulate sub-bituminous coalto produce a pumpable slurry, the energy content of the resulting diluteslurry may not reach an energy level capable of sustaining an efficientgasification operation.

In some known IGCC systems, the quantity of water needed to make apumpable slurry far exceeds the amount of water needed for thereactions. Although some of the water does react with the coal andconvert the coal to syngas, most of this excess slurry water passesthrough the gasifier, consuming some of the thermal energy in thereactor as the water heats up to reaction temperature, and thendegrading that thermal energy produced in the gasifier to lowertemperature levels as the product gas is cooled in downstream equipment.The extra energy required for heating the excess water to gasifierreaction temperature comes at the expense of burning some of the CO andH₂ in the product syngas to CO₂ and H₂O. This requires additional oxygento be fed to the gasifier, which decreases efficiency and increasescapital cost. Also, by converting some of the CO and H₂ in the productsyngas to CO₂ and H₂O in order to heat up the excess water, the amountof CO and H₂ produced per unit of coal gasified decreases. Therefore, inorder to fuel the power block with a fixed amount of CO and H₂, thesyngas components with fuel value, a larger amount of coal must begasified when feeding a coal slurry compared with feeding coal in a muchdrier state. This increased coal requirement both decreases the plantefficiency and increases its capital cost.

Some known combustion turbines must burn a fixed amount of carbonmonoxide and hydrogen to achieve their maximum rated power production.To produce the required amount of CO and H₂, a plant feeding a diluteslurry of sub bituminous coal must gasify significantly more coal than aplant feeding a slurry of bituminous coal. Such a sub-bituminous coalplant may be both less efficient and more costly to construct andoperate.

Some known IGCC systems feed high moisture content coal to gasifiersusing a system known as a dry feed system to overcome the difficulty ofproducing a high energy content slurry and to avoid the negative impacton overall plant efficiency. In such a dry feed system, lower rank coalsmay be dried to remove two-thirds, or more, of the inherent moisturepresent in the coal. The deep drying facilitates improving the flowcharacteristics of the dried solids in the dry feed system equipment aswell as improving the overall efficiency of the gasifier. For instance,high levels of drying are often needed to help reduce the potentialconsolidation and subsequent flow problems that can result duringpressurization of higher moisture content solids in a lock hopper.However, drying the coal may consume a large amount of energy, whichreduces the overall power production of the plant as a result. Inaddition, the dry feed system equipment, which may include a compressor,lock hoppers, lock hopper valves, drying equipment and additionalstorage capacity, results in a relatively expensive system when comparedwith slurry-based systems. Furthermore, such systems are limited torelatively modest pressures, on the order of 400 psig or less, becausethe consumption of gas used for lock hopper pressurization and particlefluidization increases dramatically as system pressures increase.

SUMMARY

In one aspect, a fuel feed system for use in a gasification system isprovided, wherein the fuel feed system includes a feed preparationsection, a pressurization and conveyance section, and a slag additivesection. The feed preparation section is configured to adjust a moisturecontent within a particulate fuel and grind the fuel to a predeterminedsize. The pressurization and conveyance section is coupled in flowcommunication with the feed preparation section, and includes at leastone solids pump configured to receive a flow of the particulate fuel ata first pressure and discharge the particulate fuel at a secondpressure. The slag additive section is configured to feed a slagadditive mixture into the gasifier and substantially control a totalwater content within the gasification system as well as the melting andflow characteristics of the particulate fuel ash.

In another aspect, a gasification system is provided that includes agasifier, and a fuel feed system coupled in flow communication upstreamof the gasifier. The fuel feed system includes a feed preparationsection, a pressurization and conveyance section, and a slag additivesection. The feed preparation section is configured to adjust a moisturecontent within a particulate fuel and grind the fuel to a predeterminedsize. The pressurization and conveyance section is coupled in flowcommunication with the feed preparation section, and includes at leastone solids pump configured to receive a flow of the particulate fuel ata first pressure and discharge the particulate fuel at a secondpressure. The slag additive section is configured to feed a slagadditive mixture into the gasifier and substantially control a totalwater content, and further control melting and flow characteristics of aquantity of particulate fuel ash within the gasification system withinthe gasification system.

In yet another aspect, a method of start-up for a gasification system isprovided. The method includes using a startup fuel, for example coalconveyed by nitrogen or natural gas, and a startup mixture of slagadditive slurry, both of which are replaced following gasifier startup.The flow rates of the startup fuel and the slag additive slurry are bothestablished in circulation loops external to the gasifier prior tostartup. Gasifier startup is initiated by channeling the startup fuel,slag additive slurry and oxygen into the gasifier in a defined sequenceand in such a way that a heat source within the gasifier rapidly ignitesthe gasification reactions. Once gasification operations have stabilizedand CO2 is recovered from the syngas, the startup fuel is replaced withCO2-conveyed coal, and the startup mixture of slag additive slurry isreplaced with a slurry of slag additive and recycled fine slag and char.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a portion of an exemplary IGCC powergeneration plant that includes an exemplary fuel system.

FIG. 2 is a process flow diagram of an exemplary feed preparation systemused with fuel system shown in FIG. 1.

FIG. 3 is a process flow diagram of an exemplary feed pressurization andconveyance system used with the fuel system shown in FIG. 1.

FIG. 4 is a process flow diagram of an exemplary slag additive systemused with the fuel system shown in FIG. 1.

DETAILED DESCRIPTION

FIG. 1 is a block diagram of a portion of exemplary IGCC powergeneration plant 50. In the exemplary embodiment, plant 50 includes afuel feed system 110, an air separation unit 112 coupled in flowcommunication with fuel feed system 110, a gasification plant 114coupled in flow communication with feed system 110, and a power block116 coupled in flow communication with gasification plant 114 and IGCCpower generation plant 50. During operation, air separation unit 112uses compressed air to generate oxygen for use by gasification plant114. More specifically, air separation unit 112 separates compressed airreceived from an external source (not shown) into separate flows ofoxygen and a gas by-product, typically nitrogen. In the exemplaryembodiment, gasification plant 114 converts solid fuel and oxygen into aclean fuel gas that is burned in power block 116 to produce electricalpower, as will be described in more detail herein. It will be clear tothose skilled in the art that this diagram is a simplified version of anIGCC power plant block flow diagram and that, for the sake of clarity inexplanation, not all of the equipment blocks nor all of the connectinglines found in such a power plant have been shown in the diagram.

A solid carbonaceous fuel (not shown) is channeled into a feedpreparation section 118 of feed system 110 via a conduit 120. In theexemplary embodiment, the solid carbonaceous fuel is coal.Alternatively, the fuel may be a petroleum coke, a biomass, or any othersolid carbonaceous fuel that will enable IGCC power plant 50 to functionas described herein. In another embodiment, a slag additive may beintroduced with the solid fuel within conduit 120. Feed preparationsection 118 converts the as-received fuel into a solid particulategasifier feed with a target particle size distribution and internalmoisture content suitable for use in IGCC plant 50. Low pressurenitrogen from air separation unit 112 enters feed preparation section118 via conduit 122, a portion of which is used to convey the solidparticulate feed material to a pressurization and conveyance section 124via conduit 126. The remaining portion of the low pressure nitrogen isheated in feed preparation section 118 and channeled via conduit 128 topressurization and conveyance section 124 for use in moisture and finescontrol within section 124. Low pressure nitrogen used in thepressurization and conveyance section 124 is channeled back to feedpreparation section 118 via conduit 130 to be filtered, whichfacilitates removing particulate fines, and is then dried to facilitateremoving substantially all water therein, so that the low pressurenitrogen may be reused for various purposes throughout feed system 110.As an alternate to low pressure nitrogen, any gas can be used thatallows for the safe and reliable conveyance of the coal in accordancewith the feed system described herein.

In the exemplary embodiment, gasification plant 114 includes an acid gasremoval section 132 coupled in flow communication with a gasifier 134.Acid gases, such as H₂S COS and CO₂, are removed from a quantity of rawsyngas to produce a clean fuel gas that is channeled to a combustor 136located in power block 116 via conduit 138 for producing electricalpower, as described in more detail herein. Acid gas removal section 132produces a byproduct sulfur stream 140 and a sour, CO₂-rich gas stream142 that is compressed and recycled to feed system 110 and that is usedas the high pressure conveying gas for transporting the solidparticulate fuel into gasifier 134. The CO₂ recovered from the syngaswithin acid gas removal section 132 is compressed and channeled to feedpreparation section 118 via conduit 142. This recycled CO₂-rich gasstream is heated within feed preparation section 118 and then channeledvia conduit 144 to pressurization and conveyance section 124 for use asthe high pressure pneumatic conveying gas that transports theparticulate solid fuel into gasifier 134 via feed conduit 146. In theexemplary embodiment, high pressure nitrogen from air separation unit112 is channeled to feed preparation section 118 via conduit 148. In thepreferred embodiment, this nitrogen stream, is only used during startupwhen recycled CO₂-rich gas is not yet available (as described in moredetail herein), is preheated and then channeled via conduit 144 topressurization and conveyance section 124 for use as a high pressurepneumatic conveying gas during gasifier startup. Alternatively, any highpressure gas is used during startup that allows for the safe andreliable operation of the gasification system as disclosed herein.Further alternatively, any high pressure gas is used during normaloperation that allows for the safe and reliable operation of thegasification system as disclosed herein.

In the exemplary embodiment, feed system 110 includes a slag additivehandling section 152 that receives a slurry of char (i.e. unconvertedsolid particulate fuel) and fine slag via conduit 154 from a char andfines handling section 156. This fine particulate material is recoveredas a dilute aqueous slurry from gasification plant 114. The charfraction of this slurry is the unconverted carbon from gasifier 134, andis subsequently recycled via conduit 154. Slag or mineral additive ischanneled from an externally located storage section (not shown) to slagadditive handling section 152 via conduit 158. The mineral additive ispulverized in a dry rod or ball mill (not shown in FIG. 1) and mixedwith the char and fine slag slurry to make a final additive slurry thatis channeled by a positive displacement pump (not shown) into gasifiervia conduit 160. In an alternative embodiment, a secondary water stream162 may be used to add water to the final additive slurry fed togasifier 134 to control temperatures and modify reaction chemistry. In afurther alternative embodiment, the mineral additive is fed as drysolids to gasifier 134, in a mixture with the dry particulate fuel orusing a separate feed system with a dry solids pump and conveying gas.In a still further alternative embodiment, the mineral matter is fed togasifier 134 as a separate slurry, separate from the recycle solidsslurry. In yet another alternative embodiment, the mineral matter isprocured as a preground additive and blended with the recycle solidsslurry. In an even further embodiment, the mineral additive is anymineral-containing material that facilitates the operation of thegasification system as described herein. Alternatively, no mineraladditive is used and only a quantity of recycled char and fines, orliquid water alone is channeled to gasifier 134 via a separate conduit165.

During operation, air separation unit 112 separates oxygen from air toproduce a relatively high purity (about 95% by volume O₂) oxygen feedfor use within gasifier 134. A first portion of air enters the airseparation unit 112 directly via conduit 164. A remaining portion of airis extracted from the combustion turbine air compressor 196 conduit 166.In the exemplary embodiment, the first portion of air is about 50% ofthe total quantity of incoming air. Alternatively, the first portion ofair may be any percentage of the total quantity of air that enables fuelfeed system 110 to function as described herein. In addition toproducing the gasifier oxygen feed, air separation unit 112 alsoproduces nitrogen for use within feed system 110. The remaining nitrogenrich byproduct gas is returned via conduit 168 to the combustion turbine192 for use as a diluent gas by combustor 136.

In the exemplary embodiment, feeds channeled to gasification plant 114include pneumatically conveyed particulate solid fuel via conduit 146,slag additive, char and fine slag slurry via conduit 160, and highpurity oxygen from air separation unit 112 via conduit 170. Duringoperation, gasifier 134 converts the feeds into raw syngas that issubsequently channeled to acid gas removal section 132 via conduit 172.A coarse slag (not shown) that is separated from the syngas withingasification plant 114 is recovered as a byproduct slag stream 174. Anyunconverted carbon is recovered along with fine slag as a dilute slurryand channeled via conduit 176 to handling section 156. High pressuresteam generated by the cooling of the hot syngas effluent from gasifier134 is channeled via conduit 178 to power block 116 wherein the highpressure steam is expanded through a steam turbine 180 to produceelectrical power. In the exemplary embodiment, a process water stream(not shown) is channeled as a dilute slurry 182 to a treating section184 that treats the water to control the concentrations of variouscontaminants in the circulating process water system, including but notlimited to dissolved and suspended solids, and subsequently returns thetreated water stream to gasifier 134 for reuse via conduit 186. A cleanstream of water (not shown) is channeled from treating section 184 viaconduit 188 to disposal or beneficial use beyond the plant boundary. Adilute slurry (not shown) of fine solids removed from the water streamduring cleaning is channeled via conduit 190 to handling section 156. Inan alternative embodiment, the char and fines are not recycled to thegasifier or are only partially recycled to the gasifier. Instead, theportion of char and fines not recycled to the gasifier is channeled fromchar & fines handling system 156 via a separate conduit, not shown, todisposal or beneficial use. In a further embodiment, all or a portion ofthe char and fines are dried before recycle to the gasifier and fed tothe gasifier in combination with the coal, in combination with the dryslag additive or as a separate stream. In a still further alternative,the char and fines are recovered from the gasification system using dryscrubbing technology, and all or a portion are recycled to the gasifierin combination with the coal, in combination with the dry slag additiveor as a separate stream.

In the exemplary embodiment, power block 116 includes a combustionturbine 192 and a steam system 194. Combustion turbine 192 includes anair compressor 196 operatively coupled to a power expansion turbine 198and an electrical power generator 200 via a single shaft 202. Duringoperation, the combustion turbine 192 produces power by burning cleanfuel gas 138 using, for example, a Brayton Cycle, and steam system 194produces power by expanding steam through a steam turbine 180 using, forexample, a Rankine Cycle. More specifically, clean fuel gas 138 fromcompressor 196 and diluent nitrogen 168 (used to control NO_(x)formation) are channeled to combustor 136 and mixed and combustedtherein, wherein the exhaust gaseous products of combustion are expandedthrough expansion turbine 198, thereby turning shaft 202, which in turnoperates compressor 196 and generator 200 and electrical power isproduced therein. Hot exhaust gas from expansion turbine 198 ischanneled through a heat recovery steam generator (HRSG) 204. A highpressure steam generated as the hot exhaust gas cools is combined withhigh pressure steam 178 generated in syngas cooling section ofgasification plant 114 and channeled to steam turbine 180 where it isexpanded to make additional electrical power via generator 206. Theexpanded steam is then condensed within a condenser 208 to produceboiler feed water, which is subsequently channeled to HRSG 204 and thesyngas cooler in the gasification plant 114.

FIG. 2 is a process flow diagram of an exemplary feed preparation system118 used with fuel feed system 110 shown in FIG. 1. More specifically,FIG. 2 illustrates five flow configurations that may be used with fuelfeed system 110. In the exemplary embodiment, a volume of sub-bituminouscoal, for example Powder River Basin (PRB) coal, not shown, is channeledto feed preparation section 118 via conduit 120 and is conveyed throughan air stripping tube 210 wherein the volume of coal is contacted by acounter-current flow of low pressure nitrogen 212 being channeledthereto from a nitrogen storage drum 214. Low pressure nitrogen 212strips residual air from the interstitial spaces between the incomingpieces of coal. In the exemplary embodiment, the coal is maintained in anitrogen-rich atmosphere in all equipment operatively coupled downstreamfrom tube 210. Alternatively, any suitable inerting gas, such as CO₂ orvitiated air, may be used to maintain coal in a low oxygen-contentenvironment. The nitrogen and associated particulate matter exiting airstripping tube 210 is filtered in a dust control unit 216 prior to beingexhausted to the atmosphere. This exhaust valve point is a main losspoint for low pressure nitrogen from system 110, and the flow ofnitrogen exhausting through dust control unit 216 is the major factordetermining the makeup rate 218 from air separation unit 112 (shown inFIG. 1). In the exemplary embodiment, air stripping tube 210 includes aplurality of downwardly sloping baffle plates (not shown) positionedwithin air stripping tube 210 to facilitate creating a counter-currentof nitrogen and particles within tube 210. In an alternate embodiment,air stripping tube 210 may be a featureless column. In another alternateembodiment, air stripping tube 210 may be any configuration thatfacilitates the stripping of air from the coal in the fuel systemdisclosed herein, including configurations involving purged air locksand other configurations well known to those skilled in the art.

Coal drops through air stripping tube 210 onto a weigh belt feeder 220that is operatively coupled downstream from tube 210 and that is used tometer the coal into a cage mill 222. In the exemplary embodiment, cagemill 222 grinds the coal to a desired particle distribution in a singlestep. Alternatively, a two-step grinding process (not shown) may be usedthat utilizes a hammer mill followed by a cage mill. In the exemplaryembodiment, a target particle size distribution for the coal is about50% to about 80% filtered through a 100 mesh screen and about 100%filtered through a 10 mesh screen. Alternatively, any appropriategrinding equipment may be used in light of the type of coal feed withinfuel feed system 110, and that enables fuel feed system 110 to functionas described herein.

In the exemplary embodiment, a low pressure nitrogen gas or othersuitably inert gas purge stream 224 maintains a supply of gas purge onthe grinding equipment to prevent buildup of coal fines and to removemoisture liberated from the coal by the cleaving of coal particles andevaporated from the coal by the heat of grinding. Purge stream 224 iscombined with spent purges from other parts of the system, and thecombined stream is channeled through dust filter 226, compressed inblower 228 and channeled to inert gas drying package 230. Filter 226facilitates substantially removing fine coal dust from the purge stream224, and drying package 230 substantially removes all moisture from thepurge stream 224. Inert gas is then recycled to storage drum 214 forreuse within system 110, and condensed water from the inert gas dryingpackage 230 is recycled for use elsewhere in the plant or routed to anexternally located wastewater treatment unit (not shown). In analternative embodiment, condensed water from inert gas drying package230 may be recycled (not shown) for use elsewhere in gasification system50, such as but not limited to the additive slurry tank 406, describedlater. In another alternative embodiment, inert gas drying package 230is not used to substantially dry the inert gas, but is an inert gashumidity and temperature control unit that adjusts the humidity andtemperature of the inert gas as needed to help maintain the coal withinfuel feed system 110 at a desired moisture level content.

In the exemplary embodiment and in one exemplary flow configuration (1),ground coal particles are channeled via conduits 232, 234 and 236 intoan inlet 238 of a main coal storage silo 240. In the exemplaryembodiment, silo 240, and conduits 232, 234 and 236 are insulated tosubstantially prevent cooling of the coal and condensing of any moistureliberated by the grinding process. A stream of low pressure nitrogen orother inert gas 242 is channeled from drum 214 and enters a purge gasinlet 244 in storage silo 240. During operation, the nitrogen or inertgas flow 242 may be used to fluidize a lower portion 246 of storage silo240 to enable the solids to flow of out of silo 240. It also maintains asufficiently inert environment throughout silo 240 to substantiallyprevent spontaneous combustion therein. And as it rises upwards throughsilo 240, the nitrogen or inert gas flow 242 strips away any excess,residual moisture from the coal solids that may have been liberatedduring the grinding process and thus substantially prevents moisturefrom re-condensing as the coal particles cool.

In the exemplary embodiment, coal is channeled from an outlet 248positioned on the bottom 246 of storage silo 240 and is metered into apneumatic pick-up station 250 where the coal is entrained in a flow oflow pressure nitrogen gas 252 channeled from the drum 214. The nitrogenor other inert gas 252 transports the coal particles via dense phasepneumatic transport in conduit 126 to feed pressurization and conveyancesystem 124 (shown in FIG. 1). In an alternative embodiment, the coalparticles may be transported by any means that facilitates the operationof the fuel feed system 110 as described herein.

In the exemplary embodiment, feed preparation section 118 includesequipment for heating gas used in conveying coal and for reducingmoisture therein. More specifically, low pressure nitrogen or otherinert gas from drum 214 is heated in a low pressure coil 256 of anatural gas-fired heater 258. Alternatively, a conduit 260 is configuredto bypass coil 256 and is used to adjust the final temperature of theheated nitrogen 262. This heated low pressure nitrogen or other inertgas stream 262 is used for conveying and moisture removal in some of theother flow configurations shown on FIG. 2 as well as in downstreamequipment, as described in more detail herein. Heater 256 includes ahigh pressure gas heating coil 264 that increases a temperature of ahigh pressure conveying gas (not shown) for use in the feedpressurization and conveying section 124 (shown in FIG. 1). In theexemplary embodiment, the high pressure conveying gas is recycled sourCO₂ 266. Alternatively, the high pressure conveying gas may be highpressure nitrogen 268 channeled thereto from air separation unit 112, orthe high pressure conveying gas may be natural gas channeled theretofrom an external source (not shown). As another alternative, the highpressure conveying gas may be any gas suitable for conveying the coalwithin fuel feed system 110 and into the gasifier 134. In a furtheralternative, fired heater 256 is replaced by other heating means,including, but not limited to, direct heating by the combustion of airand natural gas or indirect heating by heat exchange with steam or otherhot process gases available from elsewhere in IGCC plant 50.

In an alternative embodiment and in the second exemplary flowconfiguration (2), a steam-jacketed paddle dryer 270 is coupled in flowcommunication between the cage mill 222 and main storage silo 240.Paddle dryer 270 is purged with low pressure nitrogen or inert gasstream 272 to remove moisture liberated during the coal drying process.Moisture-laden nitrogen or inert gas 274 then combines with nitrogen orinert gas from cage mill 222 and is processed to remove coal dust andwater vapor, as described in more detail herein. Paddle dryer 270 may beincorporated into feed preparation system 118 when a higher degree ofmoisture removal from the coal particles is desired, or when the feedcoal requires additional drying to remove surface moisture.Alternatively, the coal may be dried using other drying methods thatfacilitate operation of the fuel feed system as described herein.

In another alternative embodiment and in the third exemplary flowconfiguration (3), coal is channeled through air stripping tube 210 ontoa weigh belt feeder 220 and is channeled via conduit 275 through a chute276 into a pulverizer 278, e.g. a bowl mill. In the exemplaryembodiment, pulverizer 278 is a roller mill. Alternatively, pulverizer278 may be a bowl mill or an impact mill or any such device used togrind coal to a target particle size, and that enables fuel feed system110 to function as described herein. Low pressure nitrogen or otherinert gas, heated within heater 258 or other heating means not shown, ischanneled via conduit 280 to a pulverizer inlet 282 along with coal,where it substantially dries the coal particles to the target moisturelevel as the coal is being pulverized. For example, the final coalmoisture level can be controlled by adjusting the temperature of stream282. Other control methods include controlling the humidity and flowrate of the warm nitrogen or other inert gas. The warm nitrogen or otherinert gas carries the dried coal particles out of the pulverizer 278 andtransports them via conduit 126 to feed pressurization and conveyancesection 124 (shown in FIG. 1).

In another alternative embodiment and in the fourth exemplary flowconfiguration (4), an additional grinding mill 222 is coupled in flowcommunication between weigh belt feeder 220 and pulverizer 278. In thisembodiment, grinding mill 222 may be a hammer mill or other suitablemill when coupled in conjunction with pulverizer 278 that produces thedesired particle size distribution. Coal from the weigh belt feeder 220is crushed or pre-ground in a first step in mill 222 and then ischanneled via conduits 284 and 286 to pulverizer 278.

In another alternative embodiment and in the fifth exemplary flowconfiguration (5), coal is channeled from air purge tube 210 onto weighbelt feeder 220 and is directed into cage mill 222 for grinding. Theground coal is then channeled past paddle dryer via conduit 232 and ischanneled via insulated conduit 234 to pneumatic transport pickup point286. At this point, hot, dry, low pressure nitrogen or other inertconveying gas 288 from heater 258 entrains the ground coal particles andchannels the ground coal in dense phase transport via insulated conduit290 into a cyclone 292. Alternatively, the coal particles may betransported by any means that facilitates the operation of the fuel feedsystem as described herein. The temperature of the hot conveying gas andthe length of the insulated transport conduit 290 is such that, whencombined with the heat of grinding from cage mill 222, both surfacemoisture and a portion of the moisture internal to the pores of the coalparticles is vaporized and driven into the bulk gas phase. The amount ofvaporization is controlled by adjusting the temperature, flow rate andhumidity of stream 288.

In the fifth flow configuration, the particulate solids are separatedfrom the conveying gas in cyclone 292 and drop into a moisture strippingcolumn 294. In this embodiment, moisture stripping column 294 includes aplurality of downwardly sloping baffle plates (not shown) positionedwithin moisture stripping column 294 to facilitate creating acounter-current of nitrogen or other inert gas and particles therein.Alternatively, moisture stripping column 294 may be a featurelesscolumn. The particles then encounter a second, upwardly flowing stream296 of hot, dry nitrogen or other inert gas from heater 258 therein.This stripping gas stream 296, which flows counter-current to thedownwardly flowing coal particles, strips away residual moisture fromthe interstitial spaces between coal particles that was liberated duringthe grinding but that was not removed within the cyclone 292. Hot, drycoal particles exit stripping column 294 and enter silo 240 at inlet238. The coal is channeled via dense phase pneumatic transport withinconduit 126 to the feed pressurization and conveyance section 124 (shownin FIG. 1) as described in more detail herein. Moreover, finely groundcoal within an overhead flow 299 from cyclone 292 is channeled through asecondary cyclone 300 that returns the coal fines back to strippingcolumn 294 via a conduit 302 to an inlet 304. Excess gas from secondarycyclone 300 is channeled to dust collection system 226 where, along withthe other purges from the system, the combined gas is filtered to removesubstantially all remaining coal dust. After compression by blower 228,the gas is channeled to gas dryer 230 for removal of substantially allof the residual moisture that was present as a result of grinding anddrying the coal. The dry, particle free nitrogen or other inert gasexits dryer 230 and may then be recycled to drum 214 for reusethroughout the fuel feed system 110.

FIG. 3 is a process flow diagram of an exemplary feed pressurization andconveyance system 124 used with the fuel feed system 110 shown inFIG. 1. Particulate solids with the desired size distribution andmoisture content are conveyed from feed preparation section 122 (shownin FIG. 1) via dense phase pneumatic transport in conduit 126, asdescribed in more detail herein. A storage bin primary inlet cyclone 320separates solids from the low pressure nitrogen or other inert transportgas and discharges the solids to an inlet 322 of a storage bin inletstripping tube 324 for further processing. Overhead gas from cyclone 320is then channeled via conduit 326 through a storage bin secondary inletcyclone 328 that removes a substantial portion of entrained coal finesfrom the transport gas and channels the coal fines via conduit 330 tothe inlet 322 of stripping tube 324. Secondary cyclone 330 overhead gasis channeled via conduit 332 to a dust control system 334. Thesubstantially dust-free gas is then compressed by a blower 336 andchanneled to a nitrogen drying package 230 (shown in FIG. 2) for reusethroughout fuel feed system 110. Alternatively, drying package may be atemperature and humidity control package.

The coal particles removed by cyclones 320 and 330 enter inlet 322 andare channeled downwards against a counter-current flow of heatednitrogen or other inert stripping gas 128. In this embodiment, strippingtube 324 includes a plurality of downwardly sloping baffle plates (notshown) positioned within stripping tube 324 to facilitate creating acounter-current of nitrogen and particles therein. Alternatively,stripping tube 324 may be a featureless column. The stripping gasremoves residual moisture that may remain following grinding and drying,as is described in more detail herein. After passing through strippingtube 324, the coal particles enter a solids pump storage bin 338.

In the exemplary embodiment, storage bin 338 is configured to providecoal feed to two solids pumps 340 that operate in parallel.Alternatively, storage bin 338 may be configured to feed any number ofsolids pumps 340. As a further alternative, fuel feed system 110 can beconfigured to have any number of storage bins 338 and solids pumps 340that facilitate the operation of the fuel feed system as describedherein. In the exemplary embodiment, solids pump 340 is a rotary,converging space Solids Transport and Metering pump utilizing Stamet™Posimetric® feed technology, otherwise known as a Stamet™ solids pumpcommercially available from GE Energy, Atlanta, Ga. This pump is capableof transporting solids from atmospheric pressure to pressures well over1000 psig with a strongly linear relationship between pump rotationalspeed and solids mass flow. Alternatively, any type of pump orpressurizing conveyance device may be used that handles and pressurizessolids as described herein.

In the exemplary embodiment, a suction feed vessel 342 is coupled inflow communication between each outlet conduit 344 from storage bin 338and each solids pump 340, wherein each suction feed vessel 342 controlsthe flow of coal to each solids pump 340. More specifically, each feedvessel 342, which is designed to withstand full gasifier systempressure, includes an inlet safety valve 346 that is closed in the eventof a pump failure. Alternatively, or in cooperation with inlet safetyvalve 346, additional outlet safety valves, not shown, may be located inthe discharge line 352 of each solids pump. In the exemplary embodiment,feed vessels 342 are live-bottom vessels configured to ensure that thesuction inlet of each respective solids pump 340 is filled with coal,thereby ensuring a continuous a flow of particulate solids through eachpump. Alternatively, lines 344 are designed to provide a buffer volume,and may incorporate inlet safety valves 346 and other features, such asbut not limited to contoured and vibratory surfaces to assist with theflow of solids into the inlet of pumps 340.

In the exemplary embodiment, particulate solid fuel from suction feedvessels 342 is pressurized by solids pumps 340 to a pressure levelsufficient to enable the solids to flow through feed injector 348 andinto the gasifier 134 (not shown in FIG. 1). A high pressure stream ofnitrogen 350 from the air separation unit 112 (shown in FIG. 1), whichmay or may not be preheated, is coupled to a discharge conduit 352 ofeach solids pump 340 at two locations, a first connection 354 locatedadjacent the discharge 356 of solids pump 340, and a second connection358 positioned downstream from first connection 354. First connection354 provides a flow of seal nitrogen that traverses backwards throughthe compacted solid particles moving through solids pump 340. Althoughgas leakage backwards through solids pump 340 is minimal, the sealnitrogen prevents leakage of conveying gas, oxygen or syngas backwardsthrough the pump. Second connection 358 provides a relatively highervelocity jet of nitrogen directed at the particulate solids emergingfrom the solids pump discharge 356. The high speed jet breaks upoccasional agglomerations of particles and provides a substantially evendistribution of the particulate fuel that exits the solids pump 340 andfurther enables the solids to transition from the highly compactedcondition inside the pump to the free flowing fluidized conditionrequired for high pressure pneumatic transport downstream of solidspumps 340. In the preferred embodiment, the high pressure pneumatictransport of coal downstream of the solids pump 340 is dilute phasetransport. Alternatively, the high pressure pneumatic transport of coaldownstream of solids pump 340 is of any type that facilitates operationof the fuel and gasification systems. As an alternative to the highspeed jet, any mechanical delumping device may be used at any point onconduit 352 that will enable fuel feed system 110 to function asdescribed herein.

In the exemplary embodiment, following the delumping operation, the coalparticles are channeled via discharge conduit 352 into a pneumatictransport conduit 360. Therein, a high pressure conveying gas 362 fromheater 258 (shown in FIG. 2) entrains the coal solids via dilute phasepneumatic conveyance directly to the gasifier feed injector 348 viaconduits 364, 366 and 380. Solids flow control herein is achieved byvarying the speed of operation of solid pumps 340 and/or the flow,pressure and temperature of the high pressure conveyance gas. In analternate embodiment, the high pressure carrier gas is not heated. In afurther alternate embodiment, the high pressure carrier gas is processedany way that facilitates operation of the fuel and gasification systemsas described herein.

In an alternative embodiment, the solids are channeled via conduit 368into a high pressure feed vessel 370 that serves as a buffer in theconduit between solids pumps 340 and gasifier feed injector 348. Duringoperation, feed vessel 370 is an alternative flow path that may be usedto improve solids flow to gasifier 134 (not shown in FIG. 1). Feedvessel 370 may help minimize the effects of temporary flow variations orinterruptions at the solids pumps 340, or in the alternative embodimentwhere solids pumps 340 are not Posimetric pumps that may not have thesame or substantially the same continuous flow characteristics as thePosimetric technology described herein.

During operation of feed vessel 370, and in one embodiment, a portion ofa high pressure conveying gas is diverted via conduit 324 from thesolids transports conduit 360 and channeled via conduit 372 to a bottomportion 376 of the feed vessel 370 to fluidize the solids and enhanceflow characteristics thereof. A remainder 378 of the high pressureconveying gas is used to channel the solids out of feed vessel 370 andinto conduits 366 and 380 towards feed injector 348. In this embodiment,flow control is achieved by adjusting the operational speed of solidspumps 340 and by adjusting the flow rates of the high pressure conveyinggas streams 372 and 378 that are channeled to the bottom 376 of feedvessel 370.

In another alternative embodiment, it may be necessary to recycle moresour CO₂ gas to the gasifier 134 (shown in FIG. 1) than is needed toconvey the solids or that can be handled by the solids conveyanceconduits. In this embodiment, an additional conduit 382 and 384 isavailable for feeding gas directly to the feed injector 348. Thisadditional volume of gas may be used to moderate the temperature withingasifier 134 (not shown in FIG. 3), to modify the spray characteristicsof the feed injector 348, or to modify the chemistry of the gasificationreactions.

FIG. 4 is a process flow diagram of an exemplary slag additive handlingsection 152 used with the fuel feed system 110 shown in FIG. 1. In theexemplary embodiment, slag additive handling section 152 includes a slagadditive mill 402, such as a rod mill or ball mill, that receives aquantity of slag additive (not shown) from an externally located source(not shown) via a slag additive weight belt feeder 404. A slagadditive/recycle fines mix tank 406 is coupled downstream and in flowcommunication from mill 402. More specifically, slag additive is groundto the target particle size distribution within mill 402, which, in theexemplary embodiment, operates in a dry mode. Alternatively, any type ofmill that facilitates operation of the fuel system described herein maybe used. Fugitive emissions from mill 402 are captured in a dustcollection system 408.

In the exemplary embodiment, char and fines slurry is channeled viaconduit 154 from handling section 156 (shown in FIG. 1) into the mixtank. Dry particulate additive from the mill 402 is mixed with the charand fines slurry within mix tank 406 by an agitator 410. A plurality ofconduits 412 and 414 form a continuous loop 416 through which a mix tankpump 418 circulates slag additive/recycle fines slurry past the suctionof charge pump 420 to ensure that the charge pump always has an adequatesupply of slurry and to provide additional mixing in tank 406. Slurry iswithdrawn from the suction recirculation loop 416 into charge pump 420positioned downstream from mix tank pump 406. In the exemplaryembodiment, charge pump 420 is a high pressure positive displacementpump that feeds the slurry via conduit 422 to gasifier feed injector 348(shown in FIG. 3). Once the moisture level of the solid fuel beingchanneled to gasifier 134 (shown in FIG. 1) has been set by theoperation of the feed preparation section 118, the final, total amountof water fed to gasifier 134 can be controlled by adjusting the slurryconcentration of the char and fines slurry and/or the amount of freshwater makeup 424 added to mix tank 406. Alternatively, the slag additivemay be ground together with the recycle solids in a wet rod or ball millrather than grinding the slag additive separately and then blending itwith the recycle solids. The product from such a co-grinding operationis screened and then sent to mix tank 406.

Referring now to FIG. 1, and in the exemplary embodiment, prior toignition of combustion turbine 192 and start up of gasifier 134, anothercarrier gas source must be provided until sufficient levels of CO₂ areproduced by gasifier 134 and can be recovered to maintain a running fuelfeed system 110. This secondary carrier gas may by necessary becausetypically CO₂ cannot be recovered from the syngas until the gasifierstarts, or, in the case of a multi-train gasification operation, theremay not be sufficient CO2 available to provide the required amount ofCO2 to the operating trains as well as the train undergoing startup. Inthe exemplary IGCC plant 50, high pressure nitrogen obtained from theair separation unit 112 is not needed as a clean fuel gas diluent forclean fuel gas 138 until after gasifier 134 has been started and syngasis produced therein. In an alternative embodiment where the gasifier isintegrated into an ammonia production plant rather than an IGCC plant,the nitrogen from the air separation unit may not be needed for ammoniasynthesis until after the gasifier is started and syngas is produced.

Drum 214 is filled with low pressure nitrogen from the air separationunit 112 or from on-site storage, not shown. Coal is introduced intoinlet air purge tube 210 (shown in FIG. 2) and is subsequently ground incage mill 222, as described herein, and loaded into main coal silo 240wherein moisture by grinding is purged out by nitrogen 242. Low pressureconveying gas 252 from drum 314 entrains the coal from silo 240 tostorage bin 338, as shown in FIGS. 2 and 3. Once bin 338 is loaded, highpressure nitrogen from the air separation unit 112 is heated in heater258 and a continuous flow thereof is channeled to cyclone 386 (shown inFIG. 3) via successive conduits 144, 362, 360, 364, 366, 388 and 390.Nitrogen is channeled from cyclone 386 through the high efficiencycyclone package 392, the dust collection system 334, blower 336, the N₂dryer 230 and exhausted through a vent 394 in drum 214. Once the N₂conveying gas flow has been established at the correct rate, solidspumps 340 are started and pressurized solids are channeled to theconveying gas transport conduit 360. The dilute phase flow of solids isdirect through conduits 364, 366, 386, 388 and 390 to cyclone 386. Thecyclone 386 sends the solids back into the solids pump storage bin 338,and the nitrogen passes through nitrogen return system to drum 214. Thisoff-line operation allows the gas and solids flows to be adjusted totheir correct flow rates before introduction to the gasifier.

In the exemplary embodiment, a flow rate for the slag additive/char &fines slurry is also established. Referring again to FIG. 4, and in theexemplary embodiment, initially there is no recycle char and finesslurry available into which the particulate slag additive may be mixed.Rather, a start-up mixture of slag additive is produced with fresh waterin mix tank 406. Slurry circulation pump 418 continuously circulates thestartup slurry past the suction of the charge pump 420, and charge pump420 circulates pressurized slurry through conduit 428 back to the mixtank 406. This circulation allows the correct flow rate for the additiveslurry to be established off-line prior to startup of gasifier 134.

Following the establishment and stabilization of flow rates for additiveslurry, pneumatically-conveyed coal solids and oxygen, a block valve 426on conduit 428 closes substantially concurrently with the opening of ablock valve 430 on conduit 422, and thus slurry is transferred togasifier feed injector 348 instead of being recirculated back into mixtank 406. In the exemplary embodiment, substantially concurrentlytherewith, block valve 394 on conduit 390 closes and a block valve 396on conduit 380 substantially concurrently opens. N₂-conveyed solidstherein are transferred to the gasifier feed injector 348. When oxygenis subsequently introduced to gasifier 134, the thermal energy stored inthe gasifier 134 initiates the reactions, and syngas generation begins.As syngas is channeled downstream from gasifier 134, CO₂ recoverybegins, and the CO₂ stream is compressed and recycled to the front endof the fuel feed system 110 via conduit 142 (as shown in FIG. 1). Asmore CO₂ becomes available from gasifier 134 within conduit 142, highpressure nitrogen is progressively replaced with recycled sour CO₂ asthe high pressure conveying gas. The high pressure nitrogen then becomesavailable for use as a clean fuel gas diluent in the combustion turbinecombustor 136. However, until such a time as the full amount of highpressure nitrogen diluent becomes available at combustor 136, water orsteam may be used as a temporary, substitute diluent in the combustor.

Following start-up, and in the exemplary embodiment, unconverted carbon,i.e. char, along with fine slag begins to accumulate in the gasificationplant 114 char & fines handling section 156. The char and fines arerecovered in handling section 156 as a dilute slurry. The slurry is thenchanneled to the slag additive handling system 152. As this slurry ofchar and fines becomes available for recycle to the feed system 110, thefresh water makeup 424 to mix tank 406 is progressively replaced by thischar and fines slurry until all of the char is being recycled togasifier 134. The final, total amount of water fed to gasifier 134 iscontrolled by adjusting the slurry concentration of the char and finesslurry and/or the amount of fresh water makeup added to mix tank 406. Ifit is desired to add additional sour CO₂ gas to the gasifier followingstart-up, this may be accomplished by opening block valve 397 on conduit384.

In an alternative embodiment, high pressure nitrogen from the airseparation unit 112 may not be available for use as conveying gas duringgasifier startup. In this embodiment, compressed natural gas 267 may beused instead of the high pressure nitrogen. Natural gas may be used as abackup fuel for combustion turbine 192 and sufficient quantities may beavailable for use as a high pressure conveying gas in place of the highpressure nitrogen. In this embodiment, coal is ground, dried and loadedinto the main coal silo 240 and solids pump storage bin 338. Highpressure natural gas is then heated in heater 258 and channeled viaconduits 144, 360, 362, 364, 366, 388, and 398 to a plant flare (notshown). During startup, this allows the natural gas flow rate to bestabilized at the desired value. Gasifier 134 may then be started usingnatural gas without the use of any coal solids, since natural gas is asuitable fuel for the gasifier all by itself. Since natural gas has noash for which a slag modifier is required, the gasifier can be startedup on natural gas without having to start the slag additive system 152.

In this embodiment, gasifier 134 is started on natural gas bysubstantially simultaneously closing block valve 399 in conduit 398 andopening block valve 396 in conduit 380. Oxygen is then channeled intogasifier 134 through conduit 323. Thermal energy stored in the gasifierrefractory initiates the reactions, and syngas generation begins, asdescribed in more detail herein. In this embodiment, gasifier 134 mayoperate with natural gas as the sole feed for any practical duration oftime.

In this alternative embodiment, the introduction of solid particulatefuel begins by activating the solids pumps 340. Coal particles from thedischarge of pumps 340 drop into the solids pickup conduit 360 whereinthe coal is entrained by the flow of natural gas to gasifier feedinjector 348 via conduit 380, as described in more detail herein. Theaddition of coal to the natural gas substantially increases the flow offuel to gasifier 134, and a flow rate of oxygen to the gasifier must beincreased in order to provide an adequate amount of oxygen to gasify allof the carbon in the feed. The slag additive slurry must also be startedup so that slag additive slurry can be fed to the gasifier by closingblock valve 426 on conduit 428 and opening block valve 430 on conduit422. Gasifier 134 may run on this mixture of natural gas and coal forany practical duration of time. During operation, the natural gas andcoal flow rates may not exceed the downstream demand for syngas. Morespecifically, gasifier 134 may be started up with a low flow rate ofnatural gas so that, when the coal particles are added, an amount ofsyngas is produced that satisfies the downstream process demand.Alternatively, if the gasifier operations have already been establishedat a higher than desirable rate for the transition to coal feed, thenatural gas flow may be reduced, together with an appropriatemodification of the oxygen flow rate, to allow the introduction of coalparticles into the natural gas. As syngas production continues in thegasifier, CO₂ may be recovered from the syngas, compressed and routed toconveying gas heater 258 to progressively replace the natural gas. Asthe composition of the conveying gas transitions from 100% natural gasto 100% recycled sour CO₂, the flow rate of solids into the solidspickup conduit 360 is increased to maintain substantially the same levelof fuel energy flow into gasifier 134. The flow rate of slagadditive/recycle char and fines slurry is also increased to match theincreasing flow rate of coal. Using natural gas during start-upoperations allows gasifier 134 to be started up using a clean,sulfur-free fuel, which is therefore advantageous for IGCC plantslocated in regions with process gas flaring restrictions.

Described herein is a fuel feed system that may be utilized in IGCCplants that provides a cost-effective, highly efficient and reliablesystem for supplying coal to an IGCC plant by integrating coal grinding,moisture control and a solids pump upstream of a gasifier. In eachembodiment, the fuel preparation system controls the moisture beingchanneled to the gasifier to a desired level that is between themoisture content in a dry feed system and the moisture content in aslurry feed system. More specifically, a pulverized PRB coal feed havinga well-controlled internal moisture content may be tailored to optimizenot only the gasifier performance, but also the performance of theoverall system in which the gasifier plays a central role. Further, ineach embodiment, the addition of the solids pump upstream of thegasifier facilitates pressurizing the coal from atmospheric pressure atthe pump inlet to a pressure above the gasifier operating pressure inorder to facilitate pneumatic conveyance of the coal into the gasifier.As a result, a continuous flow of pressurized coal is channeled to thegasifier. Moreover, an improved feed system is disclosed that providesan alternative to conventional dry feed systems for feeding low rankcoals, such as sub bituminous coals and lignites, to a refractory-lined,entrained-flow gasifier for the production of syngas for powergeneration in an IGCC plant. As such, a simpler, more robust method ofproviding a feed system that is similar to slurry feed systems isdisclosed that replaces the expensive lock hoppers, valves andcompressors with an alternative method of pressurizing the solids usedtherein. Accordingly, the costs associated with maintaining a dry feedsystem and the inefficiencies associated with a slurry feed system areboth avoided.

Exemplary embodiments of fuel feed systems are described above indetail. The fuel feed system components illustrated are not limited tothe specific embodiments described herein, but rather, components ofeach system may be utilized independently and separately from othercomponents described herein. For example, the fuel system componentsdescribed above may also be used in combination with different fuelsystem components.

As used herein, an element or step recited in the singular and proceededwith the word “a” or “an” should be understood as not excluding pluralelements or steps, unless such exclusion is explicitly recited.Furthermore, references to “one embodiment” of the present invention arenot intended to be interpreted as excluding the existence of additionalembodiments that also incorporate the recited features.

This written description uses examples to disclose the invention,including the best mode, and also to enable any person skilled in theart to practice the invention, including making and using any devices orsystems and performing any incorporated methods. The patentable scope ofthe invention is defined by the claims, and may include other examplesthat occur to those skilled in the art. Such other examples are intendedto be within the scope of the claims if they have structural elementsthat do not differ from the literal language of the claims, or if theyinclude equivalent structural elements with insubstantial differencesfrom the literal language of the claims.

What is claimed is:
 1. A gasification system comprising: a gasifier; anda fuel feed system comprising: a feed preparation section comprising: agrinding device for grinding a particulate fuel to a predetermined size;and a humidity control unit configured to adjust a humidity of an inertgas to control a moisture content associated with the particulate fuel;a pressurization and conveyance section coupled in flow communicationwith said feed preparation section, said pressurization and conveyancesection comprising at least one solids pump configured to receive a flowof the particulate fuel at a first pressure and discharge theparticulate fuel at a second pressure; a first conduit coupled in flowcommunication with said at least one solids pump, said first conduitconfigured to channel the pressurized particulate fuel to a feedinjector of the gasifier; and a slag additive handling sectioncomprising a pump to feed a slurry into the feed injector of thegasifier and substantially control a total water content of a quantityof feeds into the gasifier by adjusting a concentration of the slurryfed into the gasifier, and further control melting and flowcharacteristics of a quantity of particulate fuel ash within thegasification system.
 2. A gasification system in accordance with claim1, further comprising: a separation device configured to separate atleast one of moisture and air from the particulate fuel, said separationdevice comprising at least one of: one or more moisture stripping tubespositioned upstream of said solids pump, said one or more moisturestripping tubes configured to remove at least a portion of the moistureassociated with the particulate fuel; and one or more air strippingtubes positioned upstream of said one or more moisture stripping tubes,said one or more air stripping tubes configured to remove at least aportion of the air associated with the particulate fuel.
 3. Agasification system in accordance with claim 2, wherein said feedpreparation section further comprises a moisture stripping assemblycomprising a low pressure conveying line and a cyclone coupled in flowcommunication with the at least one moisture stripping tube, saidmoisture stripping assembly configured to channel a counter-flow of adrying gas against an incoming flow of particulate fuel to facilitatefurther drying of the particulate fuel, wherein at least one of thedrying gas, the low pressure conveying line and the cyclone are heated.4. A gasification system in accordance with claim 1, wherein saidgrinding device further comprises at least one mill configured to grindthe particulate fuel to a predetermined particle size distribution.
 5. Agasification system in accordance with claim 4, wherein said feedpreparation section further comprises at least one dryer assemblycoupled in flow communication with said at least one mill, said at leastone dryer assembly configured to remove moisture from the particulatefuel.
 6. A gasification system in accordance with claim 1, wherein saidgrinding device comprises a pulverizer configured to reduce a particlesize distribution of the particulate fuel; and said feed preparationsection further comprises a belt feeder configured to receive a flow offuel particulate and channel the particulate fuel to said pulverizer. 7.A gasification system in accordance with claim 6, wherein said grindingdevice of said feed preparation section further comprises a mill coupledin flow communication upstream of said pulverizer and configured togrind the particulate fuel to the predetermined particle sizedistribution.
 8. A gasification system in accordance with claim 1,wherein said pressurization and conveyance section further comprises: anoutlet conduit; and a feed vessel coupled between said outlet conduitand at least one solids pump, said feed vessel configured to smooth aflow of the particulate fuel.
 9. A gasification system in accordancewith claim 8, wherein said outlet conduit comprises a flow of a gasconfigured to facilitate providing a substantially even distribution ofthe particulate fuel exiting said at least one solids pump.
 10. Agasification system comprising: a gasification plant comprising: agasifier; and a char and fines handling device for recovering char andfine slag accumulated in the gasification plant as a dilute slurry; anda fuel feed system coupled in flow communication upstream of saidgasifier, said fuel feed system comprising: a feed preparation sectioncomprising: a grinding device for grinding a particulate fuel to apredetermined size; and a humidity control unit configured to adjust ahumidity of an inert gas to control a moisture content associated withthe particulate fuel; a pressurization and conveyance section coupled inflow communication with said feed preparation section, saidpressurization and conveyance section comprising at least one solidspump configured to receive a flow of the particulate fuel at a firstpressure and discharge the particulate fuel at a second pressure; afirst conduit coupled in flow communication with said at least onesolids pump, said first conduit configured to channel the pressurizedparticulate fuel to a feed injector of said gasifier; and a slagadditive handling section comprising a pulverizer for pulverizing amineral additive that is mixed with the dilute slurry received from thechar and fines handling device to produce an additive slurry, the slagadditive handling section further comprising a pump to feed the additiveslurry into the feed injector of the gasifier and substantially controla total water content of a quantity of feeds into the gasifier byadjusting a concentration of the additive slurry fed into the gasifier,and further control melting and flow characteristics of a quantity ofparticulate fuel ash within the gasification system.
 11. A gasificationsystem in accordance with claim 10, further comprising: a separationdevice configured to separate at least one of moisture and air from theparticulate fuel, said separation device comprising at least one of: oneor more moisture stripping tubes positioned upstream of said solidspump, said one or more moisture stripping tubes configured to remove atleast a portion of the moisture associated with the particulate fuel;and one or more air stripping tubes positioned upstream of said one ormore moisture stripping tubes, said one or more air stripping tubesconfigured to remove at least a portion of the air associated with theparticulate fuel.
 12. A gasification system in accordance with claim 11,wherein said feed preparation section further comprises a moisturestripping assembly comprising a low pressure conveying line and acyclone coupled in flow communication with the at least one moisturestripping tube, said moisture stripping assembly configured to channel acounter-flow of a drying gas against an incoming flow of particulatefuel to facilitate further drying of the particulate fuel, wherein atleast one of the drying gas, the low pressure conveying line and thecyclone are heated.
 13. A gasification system in accordance with claim10, wherein said grinding device further comprises at least one millconfigured to grind the particulate fuel to a predetermined particlesize distribution.
 14. A gasification system in accordance with claim13, wherein said feed preparation section further comprises at least onedryer assembly coupled in flow communication with said at least onemill, said at least one dryer assembly configured to remove moisturefrom the particulate fuel.
 15. A gasification system in accordance withclaim 10, wherein said grinding device further comprises a pulverizerconfigured to reduce a particle size distribution of the particulatefuel; and said feed preparation section further comprises a belt feederconfigured to receive a flow of fuel particulate and channel theparticulate fuel to said pulverizer.
 16. A gasification system inaccordance with claim 15, wherein said grinding device of said feedpreparation section further comprises a mill coupled in flowcommunication upstream of said pulverizer and configured to grind theparticulate fuel to a predetermined particle size distribution.
 17. Asystem in accordance with claim 10, wherein said pressurization andconveyance section further comprises: an outlet conduit; and a feedvessel coupled between said outlet conduit and said at least one solidspump, said feed vessel configured to smooth a flow of the particulatefuel.
 18. A gasification system in accordance with claim 17, whereinsaid outlet conduit comprises a flow of a gas configured to facilitateproviding a substantially even distribution of the particulate fuelexiting said at least one solids pump.